Modulation of neuronal circuits is key to information processing in the brain. The majority of neuromodulators exert their effects by activating G-protein-coupled receptors (GPCRs) that control the production of second messengers directly impacting cellular physiology. How numerous GPCRs integrate neuromodulatory inputs while accommodating diversity of incoming signals is poorly understood. In this study, we develop an in vivo tool and analytical suite for analyzing GPCR responses by monitoring the dynamics of a key second messenger, cyclic AMP (cAMP), with excellent quantitative and spatiotemporal resolution in various neurons...

Primaquine (PQ) is the only commercially available drug that clears dormant liver stages of malaria and blocks transmission to mosquito vectors. Although an old drug, much remains to be known about the mechanism(s) of action. Herein we develop a fluorescent tagged PQ to discover cellular localization in the human malaria parasite, Plasmodium falciparum. Successful synthesis and characterization of a primaquine-coumarin fluorescent probe (PQCP) demonstrated potency equivalent to the parent drug and the probe was not cytotoxic to HepG2 carcinoma cells...

MRI is a powerful modality to detect neuroanatomical differences that result from mutations and treatments. Knowing which genes drive these differences is important in understanding etiology, but candidate genes are often difficult to identify. We tested whether spatial gene expression data from the Allen Brain Institute can be used to inform us about genes that cause neuroanatomical differences. For many single-gene-mutation mouse models, we found that affected neuroanatomy was not strongly associated with the spatial expression of the altered gene and there are specific caveats for each model...

Studies of major depressive disorder (MDD) in postmortem brain tissue report enhanced binding to inhibitory serotonin-1A autoreceptors in midbrain dorsal raphe and reductions in length of axons expressing the serotonin transporter (SERT) in dorsolateral prefrontal cortex. The length density of axons expressing SERT in the orbitofrontal cortex (OFC) was determined in 18 subjects with MDD and 17 age-matched control subjects. A monoclonal antibody was used to immunohistochemically label the SERT in fixed sections of OFC...

The synaptic uptake of choline via the high-affinity, hemicholinium-3-dependent choline transporter (CHT) strongly influences the capacity of cholinergic neurons to sustain acetylcholine (ACh) synthesis and release. To advance research on the impact of CHT capacity in humans, we established the presence of the neuronal CHT protein in human T lymphocytes. Next, we demonstrated CHT-mediated choline transport in human T cells. To address the validity of T cell-based choline uptake as a proxy for brain CHT capacity, we isolated T cells from the spleen, and synaptosomes from cortex and striatum, of wild type and CHT-overexpressing mice (CHT-OXP)...

Serotonin (5-HT) is an important neurotransmitter in the central nervous system where it modulates circuits involved in mood, cognition, movement, arousal, and autonomic function. The 5-HT transporter (SERT; SLC6A4) is a key regulator of 5-HT signaling, and genetic variations in SERT are associated with various disorders including depression, anxiety, and autism. This review focuses on the role of SERT in the sympathetic nervous system. Autonomic/sympathetic dysfunction is evident in patients with depression, anxiety, and other diseases linked to serotonergic signaling...

Serotonin (5-hydroxytryptamine, 5-HT) has long been recognized as a key contributor to the regulation of mood and anxiety and is strongly associated with the etiology of major depressive disorder (MDD). Although more known for its roles within the central nervous system (CNS), 5-HT is recognized to modulate several key aspects of immune system function that may contribute to the development of MDD. Copious amounts of research have outlined a connection between alterations in immune system function, inflammation status, and MDD...

Selective serotonin (5-HT, SERT) reuptake inhibitors (SSRIs) are the most commonly prescribed treatments for depression. However, they have delayed efficacy and can induce side-effects that can encourage discontinuation. Recently, agents have been developed, including vortioxetine (Trintellix), that augment SERT blockade with interactions at other targets. At therapeutic doses, vortioxetine interacts with SERT as well as 5-HT1A, 5-HT1B, 5-HT3, and 5-HT7 receptors. We assessed the SERT-dependency of vortioxetine action using the SERT Met172 mouse model, which disrupts high-affinity interactions of many antidepressants with the transporter...

Some rats [sign-trackers (STs)] are prone to attribute incentive salience to reward cues, which can manifest as a propensity to approach and contact pavlovian cues, and for addiction-like behavior. STs also exhibit poor attentional performance, relative to goal-trackers (GTs), which is associated with attenuated acetylcholine (ACh) levels in prefrontal cortex (Paolone et al., 2013). Here, we demonstrate a cellular mechanism, linked to ACh synthesis, that accounts for attenuated cholinergic capacity in STs. First, we found that electrical stimulation of the basal forebrain increased cortical choline transporter (CHT)-mediated choline transport in GTs, paralleled by a redistribution of CHTs to the synaptic plasma membrane...

The monoamine neurotransmitter dopamine (DA) acts across phylogeny to modulate both simple and complex behaviors. The presynaptic DA transporter (DAT) is a major determinant of DA signaling capacity in ensuring efficient extracellular DA clearance. In humans, DAT is also a major target for prescribed and abused psychostimulants. Multiple structural determinants of DAT function and regulation have been defined, though largely these findings have arisen from heterologous expression or ex vivo cell culture studies...

Modulation of neurotransmission by the monoamines dopamine (DA), norepinephrine (NE), and serotonin (5-HT) is critical for normal nervous system function. Precise temporal and spatial control of this signaling in mediated in large part by the actions of monoamine transporters (DAT, NET, and SERT, respectively). These transporters act to recapture their respective neurotransmitters after release, and disruption of clearance and reuptake has significant effects on physiology and behavior and has been linked to a number of neuropsychiatric disorders...

This Letter describes the further lead optimization of the CHT inhibitor probe, ML352 (VU0476201), and the development of VU6001221, an improved in vivo tool. A multi-dimensional optimization effort encountered steep SAR, and ultimately, subtle tuning of the electronics of the central phenyl core provided VU6001221, a CHT inhibitor with comparable potency for choline uptake inhibition as ML352, yet improved PK and CNS penetration. Moreover, VU6001221 enabled evaluation, for the first time, of a CHT inhibitor in a standard preclinical rodent cognition model, novel object recognition (NOR)...

Biomarker, neuroimaging, and genetic findings implicate the serotonin transporter (SERT) in autism spectrum disorder (ASD). Previously, we found that adult male mice expressing the autism-associated SERT Ala56 variant have altered central serotonin (5-HT) system function, as well as elevated peripheral blood 5-HT levels. Early in gestation, before midbrain 5-HT projections have reached the cortex, peripheral sources supply 5-HT to the forebrain, suggesting that altered maternal or placenta 5-HT system function could impact the developing embryo...

Adrenal chromaffin cells (ACCs), the neuroendocrine arm of the sympathetic nervous system, secrete catecholamines to mediate the physiological response to stress. Although ACCs do not synthesize 5-HT, they express the serotonin transporter (SERT). Genetic variations in SERT are linked to several CNS disorders but the role(s) of SERT/5-HT in ACCs has remained unclear. Adrenal glands from wild-type mice contained 5-HT at ≈ 750 fold lower abundance than adrenaline, and in SERT(-/-) mice this was reduced by ≈80% with no change in catecholamines...

The basal forebrain cholinergic projection system to the cortex mediates essential aspects of visual attention performance, including the detection of cues and the response to performance challenges (top-down control of attention). Higher levels of top-down control are mediated via elevated levels of cholinergic neuromodulation. The neuronal choline transporter (CHT) strongly influences the synthesis and release of acetylcholine (ACh). As the capacity of the CHT to import choline into the neuron is a major, presynaptic determinant of cholinergic neuromodulation, we hypothesize that genetically-imposed CHT capacity variation impacts the balance of bottom-up versus top-down control of visual attention...

Autism spectrum disorder (ASD) is an increasingly common behavioral condition that frequently presents with gastrointestinal (GI) disturbances. It is not clear, however, how gut dysfunction relates to core ASD features. Multiple, rare hyperfunctional coding variants of the serotonin (5-HT) transporter (SERT, encoded by SLC6A4) have been identified in ASD. Expression of the most common SERT variant (Ala56) in mice increases 5-HT clearance and causes ASD-like behaviors. Here, we demonstrated that Ala56-expressing mice display GI defects that resemble those seen in mice lacking neuronal 5-HT...